Medvedev's trip to the disputed islands in Russia's Far East - known as the Southern Kuriles in Russia but as the Northern Territories in Japan - prompted Japan's Ministry of Foreign Affairs to complain.

Unlike Japan's dispute with China over islands in the East China Sea, which are near potentially vast maritime oil and gas reserves, the feud with Russia has more to do with the legacy of World War Two.

Soviet soldiers seized the islands at the end of the war and the territorial row has weighed on diplomatic relations ever since, precluding a formal peace treaty. – Reuters